Alterations in the fillet quality of myostatin-knockout red sea bream Pagrus major: Preliminary insights into nutritional, compositional, and textural properties.

Myostatin (MSTN) is a negative regulator of skeletal muscle growth and a popular target for enhancing the productivity of farmed fish. We previously developed an mstn-knockout breed of the aquaculture fish red sea bream (Pagrus major) using genome editing technology. However, little is known about the effects of mstn disruption on the fillet quality of red sea bream and other fish species. In this study, we used fillets of mstn-deficient red sea bream to evaluate their compositional and textural changes during refrigeration. Compared to the wild type, the mutant fillets exhibited an increase in moisture content and a decrease in drippings, indicating an enhanced water-holding capacity. Furthermore, the mutant fillets showed increased water retention and marginally lower collagen content, resulting in lower breaking force, an index of texture. In conclusion, we demonstrated that mstn disruption alters the compositional and textural properties of red sea bream fillets.

A novel liver-specific immunoglobulin heavy chain-like gene in a cartilaginous fish.

We identified a novel immunoglobulin (Ig) heavy chain-like gene (tsIgH) expressed in the liver of the banded houndshark Triakis scyllium by preliminary transcriptomic analysis. The tsIgH gene showed less than 30% of amino acid identities to Ig genes of the shark. The gene encodes one variable domain (VH) and three conserved domains (CH1-CH3) with a predicted signal peptide. Interestingly, this protein has only one cysteine residue in a linker region between VH and CH1 other than those required for the formation of the immunoglobulin domain. Genome sequencing revealed that each of the domains was encoded by a corresponding single exon, and the exon-intron structures of the homologues are conserved in the other cartilaginous fishes. By RT-qPCR analysis, the transcript of the tsIgH gene was observed only in the liver, while that of the IgM was mainly detected in the epigonal organ, liver, and spleen. The novel Ig-heavy chain-like gene in cartilaginous fish may provide new clues to the evolution of immunoglobulin genes.

Preliminary characterization of pathogen-detection activities of serum antibodies from the banded houndshark Triakis scyllium.

Antibodies of cartilaginous fish are of scientific interest due to their phylogenetic position. In the present study, we developed antiserum against IgM of the banded houndshark, Triakis scyllium, and characterized binding activity of the IgM against fish pathogenic bacteria. Pentameric and monomeric IgM antibodies were separated by gel filtration chromatography using high performance liquid chromatography and SDS-PAGE. Antisera were developed by immunizing rabbits with unfractionated IgM antibodies separated by SDS-PAGE electrophoresis. Shark serum antibodies were found to have binding affinity for Aeromonas hydrophila, Vibrio anguillarum, Edwardsiella tarda, and Pseudomonas plecoglossicida antigens but not Lactococcus garvieae by enzyme-linked immunosorbent assay. We speculate the binding activities of shark antibodies may confer protection against certain bacterial pathogens.

Suitability of hybrid mackerel (Scomber australasicus × S. japonicus) with germ cell-less sterile gonads as a recipient for transplantation of bluefin tuna germ cells.

We aim to establish a small-bodied surrogate broodstock, such as mackerel, which produces functional bluefin tuna gametes by spermatogonial transplantation. When reproductively fertile fish are used as recipients, endogenous gametogenesis outcompetes donor-derived gametogenesis, and recipient fish predominantly produce their gametes. In this study, we assessed fertility of hybrid mackerel, Scomber australasicus × S. japonicus, and its suitability as a recipient for transplantation of bluefin tuna germ cells. Hybrid mackerel were produced by artificially inseminating S. australasicus eggs with S. japonicus spermatozoa. Cellular DNA content and PCR analyses revealed that F1 offspring were diploid carrying both paternal and maternal genomes. Surprisingly, histological observations found no germ cells in hybrid mackerel gonads at 120 days post-hatch (dph), although they were present in the gonad of 30- and 60-dph hybrid mackerel. The frequency of germ cell-less fish was 100% at 120-dph, 63.1% at 1-year-old, and 81.8% at 2-year-old. We also confirmed a lack of expression of germ cell marker (DEAD-box helicase 4, ddx4) in the germ cell-less gonads of hybrid mackerel. By contrast, expression of Sertoli cell marker (gonadal soma-derived growth factor, gsdf) and of Leydig cell marker (steroid 11-beta-hydroxlase, cyp11b1) were clearly detected in hybrid mackerel gonads. Together these results showed that most of the hybrid gonads were germ cell-less sterile, but still possessed supporting cells and steroidogenic cells, both of which are indispensable for nursing donor-derived germ cells. To determine whether hybrid gonads could attract and incorporate donor bluefin tuna germ cells, testicular cells labeled with PKH26 fluorescent dye were intraperitoneally transplanted. Fluorescence observation of hybrid recipients at 14 days post-transplantation revealed that donor cells had been incorporated into the recipient's gonads. This suggests that hybrid mackerel show significant promise for use as a recipient to produce bluefin tuna gametes.